1. Field of the Invention
The present invention relates to a grasping apparatus installed in, for example, a robot and used to transfer physical objects or assemble structural members and, more particularly, to a grasping apparatus that has a simple structure, can be driven by a small number of actuators, and is applicable to various physical objects.
2. Description of the Related Art
In recent years, research and development of robots have been actively performed mainly for the purpose of replacing human work. Many robots have grasping apparatuses in their hand units to transfer physical objects or assemble structural members.
The grasping apparatus has many joint degrees of freedom to perform complicated work. If the number of actuators for driving joints increases, however, the weight of the actuators and the frame supporting the actuators increase and the grasping apparatus becomes large-sized. The driving and control circuits and wiring for operating the actuators also increase in size with the number of the actuators, thereby making driving software complicated so as to synchronously control a plurality of joint shafts. Since a single actuator achieves only one degree of freedom such as rotation or parallel movement, many actuators are necessary to support various physical objects.
For example, Japanese Unexamined Patent Application Publication No. 2008-105116 proposes a two-fingered grasping robot hand having a blade spring and an actuator. Even when the torque of the actuator is 0, this robot hand can grasp a physical object using a spring force. However, the problem is that an inside force is generated at all times and grasping only in the pivotal direction is enabled.
In addition, for example, Japanese Unexamined Patent Application Publication No. 2008-49456 proposes a robot hand having one actuator, located at the base, that opens or closes the finger middle joint and finger base joint using a gear train to open or close the left and right fingers synchronously. However, a backlash occurs in this robot hand because power is transferred with the gear train. Another problem is that grasping is enabled only in the rotation direction of a link, which is equivalent to a finger.
In addition, for example, Japanese Unexamined Patent Application Publication No. 2007-69286 proposes a robot hand that synchronously opens or closes the left and right fingers using a differential gear and a wire via a pulley. However, one problem with this robot hand is the initial tension and the elongation of the wire itself because power is transferred by the wire. Another problem is a backlash or efficiencies because a bevel gear is used.
For example, Japanese Unexamined Patent Application Publications Nos. 2005-238400 and 2005-261535 propose grasping apparatuses that have two mutually facing fingers of a gripper, each of which includes parallel links. This type of grasping apparatus grasps a physical object by opening or closing the claws at the tip of the fingers with their grasping surfaces kept substantially parallel. Therefore, even when the physical object is box-shaped, the contact area between the claws and the physical object can be reserved sufficiently regardless of the size of the box.